Method for preparing crimped acrylonitrile polymer fibers



June 6, 1961 s. RQSENBAQM Em 3,324, 5

METHOD FOR PREPARING CRIMPED ACRYLONITRILE POLYMER FIBERS Filed Nov. 20, 1963 INVENTORS. Jh/omo Rosenbaum Gare/0Q. L asser- United States Patent 3,324,215 METHOD FOR PREPARING CRIMPED ACRYLONITRILE POLYMER FIBERS Shlomo Rosenbaum and Gerald L. Losser, Williamsburg,

Va., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Nov. 20, 1963, Ser. No. 325,002 7 Claims. (Cl. 264-168) This invention relates to a method for preparing acrylonitrile polymer filamentary structures, particularly fibers, in a naturally crimped condition that is, fibers that are obtained in a crimped condition without the imposition thereto of a mechanical crimping force.

It is well known that most synthetic polymer fibers are crimped or otherwise texturized to create a more desirable aesthetic appearance from the standpoint of visual appearance and the hand or feel of the fiber. Such treatments are ordinarily given the fibers because the synthetic fibers have a more or less slick or waxy feel and glossy appearance which are objectionable for use in wearing apparel and other textile end uses. Also, as in the instance of acrylonitrile polymer fibers which are often employed with wool in blends or are employed as the sole fibrous constituent of a fabric for applications wherein wool is ordinarily employed, it is important that the fabric containing the acrylonitrile polymer fiber have or approach the properties of wool regards appearance, feel, resilience and bulk. Wool in its natural state is crimped or kinkly which provides it with good and permanent resilience and high-bulk or covering power. It is also found necessary that when synthetic fibers are to be processed on wool textile processing equipment that the fibers need to be crimped to provide interlocking points and to prevent the fibers from flying apart during such processing as carding.

Various methods have been used for providing acrylonitrile polymer fibers with a crimped structure. For the most part, the known and successful methods have been accomplished through the application of external mechanical forces to the fibers. For example, passing a bundle of the fibers between a pair of co-acting gears has been employed to impart a crimped structure to the fibers. In US. Patents 2,575,781, 2,575,838, 2,686,339, and, 2,854,701 are disclosed various modifications of injecting a bundle of synthetic polymer filaments into a stufiing box wherein the filaments are forced to fold back and forth in a Zig-Zng fashion to impart a crimped structure to the fibers. These patents also teach that it is or-' dinarily necessary to heat the filaments while crimping them in such stufiing box arrangements by the use of either dry or steam heat. In US. 2,917,806 is disclosed a method for crimping acrylonitrile polymer fibers while they are in an aquagel condition which comprises forcing the gel filaments into a stuffing box crimper and causing them to fold back and forth in a manner analogous to the aforementioned patents. While the methods disclosed in the above patents ordinarily provide adequate crimping of the fibers, the crimp is more or less in one plane so that bulk is increased in essentially only two directions. Additionally, the crimp that is imparted by these methods generally creates rather sharp angle points in the fibers so that undue entanglement of the fibers may result, or, the severity of the crimp often causes weak spots in the fiber resulting in premature rupture or failure of the fiber, especially when a continuous filament is involved. In a more recent patent, U.S. 3,038,M0, a method is disclosed for imparting a helical crimp into acrylonitrile polymer fibers without utilizing any of the methods set out above in that no external mechanical forces as such are applied to the fibers. The method taught in this latter patent involves simultaneously extruding 3,324,215 Patented June 6, 1967 two acrylonitrile polymers of dilferent polymer composition and physical properties through the same orifice. The composite filament that is formed is subjected to the action of a shrinking agent such as boiling water. Although this method provides a useful crimped fiber it involves rather elaborate spinning arrangements and the careful preparation of two dissimilar polymers.

Therefore, it is the chief concern and primary object of the present invention to provide a means for preparing acrylonitrile polymer fibers having an excellent natural crimped structure and possessing high-bulk and good covering power characteristics by utilizing conventional textile spinning apparatus and methods and avoiding the need to subject the fibers to any crushing or otherwise deleterious mechanical action.

The above as well as additional objects and features of the present invention are accomplished by treating a wetspun and oriented acrylonitrile polymer gel fiber by a method which comprises impregnating the gel fiber while in a completely relaxed and free-to-shrink condition with an aqueous solution of caprolactam, (the lactam of omega-aminocaproic acid), mildly drying the impregnated gel fiber at a temperature between about 20 and C., contacting the mildly dried impregnated gel structure while in a relaxed condition with a hot aqueous medium, and subsequently irreversibly drying the gel structure to a characteristically hydrophobic textile fiber characterized in being naturally crimped. A particularly advantageous and beneficial feature of the invention is that the fibers so prepared are characterized in being naturally helically crimped, that is, helically formed about the longitudinal axis of the fiber, which provides excellent bulking properties.

The reasons why the present treatment provides the unusual results of not only causing the fiber to crimp when so treated but also to assume frequently the unusual generally helical configuration is not fully understood at this time. However, an explanation of why the results are obtained is not necessary to an understanding of the present invention which will be more fully explained in the ensuing description and specification and taken in conjunction with the sole figure of the attached drawing which schematically portrays a bundle of helically crimped fibers obtained by practice of the present invention.

The acrylonitrile polymer fibers prepared according to the invention are frequently observed to be helically crimped to an unusually regular and uniform extent. The fibers are resilient, provide high-bulk and the crimp is essentially permanent and not destroyed to any appreciable degree by hot-wet processing treatments. Fabrics constructed from these fibers have high bulk and are exceptionally resilient. If desired, fibers prepared by the present invention can be blended with other fibers of the same or different composition that are not crimped to provide useful fabrics possessing both dimensional stability and good covering power.

The acrylonitrile polymer gel fibers are impregnated with an aqueous solution of caprolactam and preferably while immersed in the aqueous solution and while the gel fibers are under no tension, that is, while they are in a completely relaxed and free-to-shrink condition. Undesirable results are obtained when the impregnation is carried out while the fiber is subjected to any tension from the standpoint that irregularity and non-uniformity of crimp occur in the resulting fibers, if a crimp occurs at all. Ambient temperatures may be utilized for the impregnation although elevated temperatures up to the boiling point of the solution can be employed with advantage. The time f-or the impregnation is apparently not critical since equally good results are obtained when the fiber is immersed in the caprolactam solution for only a few seconds or for a period of hours. Beneficially, as indicated, the gel fiber is impregnated after the fiber has been oriented to its desired degree and after the gel fiber has been washed essentially free of residual polymer solvent.

Generally, the degree of crimp, i.e., the number of helical crimps per unit length, increases with an increase in caprolactam concentration in the aqueous impregnating solution up to about 50 weight percent of caprolactam, based on weight of the solution. Increasing concentration beyond the 50 percent level does not appreciably increase the degree or effectiveness of the crimp. For example, when the fiber is impregnated with an aqueous solution containing about 25 weight percent caprolactam the resulting fiber may have in the neighborhood of about 10 crimps (measured as complete revolutions of the helix) per inch depending somewhat on the temperature of impregnation and irreversible drying. Beneficially, in order to obtain sufiicient crimp in the fiber, the concentration of the caprolactam should be at least about 5 weight percent, based on the weight of the solution. Preferably, an aqueous solution containing between about 15 and 30 weight percent caprolactam is utilized to impregnate the acrylonitrile polymer fibers although concentrations up to the saturation point of caprolactam in water (about 100 percent) can be employed. It is pointed out that the gel fibers that are impregnated in the practice of the present invention ordinarily contain anywhere from about 1 to about 3 or more parts of water or other inert swelling agents per weight of polymer. Generally during the impregnation the water of the gel structure is replaced by the caprolactam solution so that, in effect, often times a larger amount of caprolactam is incorporated in the fiber than the concentration represented in the solution. For example, for a gel structure which contains two parts of water per part of polymer, when this is immersed in a solution containing about 25 weight percent caprolactam, and if it is considered that all of the water of the gel structure is replaced by the caprolactam solution, then the dried fiber will contain about 33 percent of caprolactam, based on the dry weight of the fiber.

After the gel fiber has been impregnated with the caprolactam it is mildly dried at a temperature between about 20 and about 80 C. This can be accomplished by allowing the impregnated fiber to remain at about room temperature for a period of time or it can be passed through a heating oven wherein warm air is forced over the filaments or are otherwise dried by radiant heat or the like. Ordinarily the higher the temperature employed the less time required to proper-1y treat the gel fiber in this manner in order to obtain the resulting helical cri-mps. As with the impregnation step, this mild drying step should also be carried out while the gel fiber is in a relaxed condition. This can be accomplished in any convenient manner such as loosely winding the fibers on a coil so that they are in a condition completely free to shrink or by plaiting the fibers on a moving belt that passes through a heating zone. If this step of mildly drying is eliminated in the practice of the invention, the natural crimp that is normally obtained in the practice of the invention does not always occur, and if it does occur, it is usually irregular and partially formed such that the product is unacceptable for most end uses. It is to be understood that the mild drying treatment is only for the purposes the term implies, i.e., mild drying of the fiber, that is, the treatment is not to be so severe under any circumstances that the gel structure of the filament is destroyed or the gel structure is completely collapsed.

After the mild drying treatment, the aquagel filaments are treated with an aqueous medium, which is preferably water at a temperature of at least about 60-70 C. or above the wet glass transition temperature of the fiber and preferably at about 90 to 100 C., or with saturated steam. Preferably, the fibers are immersed in a boiling 4 water bath and, again, in such a condition that they are in a completely relaxed condition and free to shrink. The time for this treatment is not critical and equally good results are usually obtained when the fiber is immersed only for a matter of seconds as when it is immersed over an extended period of time. Advantageously, the treatment is only as short as is necessary to effect the creation of the natural crimp in the fibers in accordance with the ends of the invention. If desired, this immersion in an aqueous bath can be accomplished simultaneously with a dyeing process. In other words, the mildly dried fibers can be directly dyed in an aqueous bath which performs the dual function of simultaneously dyeing the fibers and carrying out that part of the invention to enable the creation of the crimp in the finally dried and thus dyed fiber.

The last step of the process is that of irreversibly drying the gel fiber to a conventional textile fiber condition. This is preferably done by drying the fiber at a temperature between about and 150 C. As with the other steps of the process, this final irreversibly drying is to be performed on the gel fiber while the fiber is in a relaxed and freely shrinkable condition. This drying can be carried out in any conventional manner such as plaiting the fiber on a moving conveyor belt which passes through a heating zone heated by forced hot air, or radiant heat and the like. Generally, the higher the drying temperature the greater the shrinkage of the treated fiber which usually imparts more crimps per lineal unit length of the fiber. Longer drying times are usually employed with the lower temperatures. Ordinarily, drying the fiber at about -140 C. for 6-10 minutes is advantageously employed.

It is important in the practice of the invention in order to obtain the uniform and reproducible helical crimps in the fibers that the steps outlined are carried out in the sequence indicated. If the sequence is changed, for example, if the irreversibly drying step is carried out before the fiber is immersed in the boiling water bath the helical crimp will not usually form, and if it does it is invariably of inferior quality.

If desirable, the crimped fibers prepared in the practice of the invention may be subsequently treated by applying thereto suitable finishes and lubricants, or by subjecting them to texturizing operations and the like, including certain heat treating or mild crimping to assist in stabilizing the helical crimp.

The fibers that are employed in the practice of the present invention are acrylonitrile polymer fibers that are fabricated from fiber-forming acrylonitrile polymers that contain in the polymer molecule at least about 80 weight percent of polymerized acrylonitrile, including homopolyrneric acrylonitrile, which are wet spun in and with systems that are adapted to utilize aqueous coagulating liquids for the spinning operation. Such systems include those wherein ethylene glycol, dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, butyrolactone and the like or the various aqueous saline polyacrylonitriledissolving solvents are employed as spinning solution solvents for the polymer and are also present in non-polymerdissolving concentrations in the aqueous coagulating liquid used in the spin bath.

The useful, known aqueous saline solvents for the various fiber-forming acrylonitrile polymers and polyacrylonitrile include zinc chloride, the various thiocyanates such as calcium, lithium bromide, salt mixtures of the so-called lyotropic series, and other recognized by the art, [as has been disclosed, among other places in United States Letters Patents Nos. 2,140,921; 2,425,192; 2,648,592, 2,648,- 593; 2,648,646; 2,648,648; 2,648,649; and 2,949,435. Advantageously, aqueous zinc chloride solutions are used for the purpose.

Thoroughly washed acrylonitrile polymer aquagel fibers, incidentally, are usually found to contain not more than 5 /2 parts by weight of water (including residual extrinsic or exterior water associated therewith) for each part by weight of dry polymer therein. More frequently, washed acrylonitrile polymer aquagel fibers are found to contain from about 2 and usually from about 3 to 4 parts by weight of water for each part by weight of polymer.

Homopolymeric acrylonitrile gel filaments or polymeric gel filaments formed from copolymerizing acrylonitrile with one or more other ethylenically unsaturated monomers copolymerizable with acrylonitrile such that the copolymeric product contains at least about 80 percent by weight of acrylonitrile polymerized in the polymer molecule may be beneficially and advantageously treated according to this invention. Examples of other monomeric materials which may be employed advantageously wit-h acrylonitrile in the practice of the present invention include alkyl alcohol, vinyl acetate, acrylamide, methacrylamide, methyl acrylate, 2-vinyl pyridine, dimethylaminoethylacrylate, methacrylonitrile, acrylic acid, itaconic acid, ethyl acrylate, fumaronitrile, 2-vinyl S-ethyl pyridine, ethylene sulfonic acid and its alkali metal salts, vinyl lactams such as vinyl caprolactam and vinyl piparidone, vinyl benzene sulfonic acid and its salts, vinylbenzenetrimethyl ammonium chloride, vinylmethyl ether, N-acrylo-yl taurine and its salts, 2-aminoethyl-methacrylate hydrochloride, 2-sulfoethylacrylate, maleic anhydride and the like, including mixtures thereof.

In order to further illustrate the invention, acrylonitrile homopolymer gel fibers were prepared by wet spinning polyacrylonitrile dissolved in an aqueous zinc chloride solution into an aqueous zinc chloride coagulation bath. The coagulated gel fibers were water washed essentially completely free of residual zinc chloride and hot stretched in an .aqueous bath about :1 to orient the molecules thereof. A bundle of the stretched gel fibers were then immersed while in a relaxed condition, in an aqueous about 25 weight percent solution of caprolactam at room temperature for about 5 minutes. The gel fibers were removed from the caprolactam solution and allowed to mildly dry in a relaxed condition at room temperature for about a week. Following the mild drying of the gel fibers at which time the fibers still retained a gel structure, the fibers were rinsed with water and placed in an aqueous dye bath at about 100 C. and dyed for several minutes. The fibers were removed from the dyebath and irreversibly dried in a relaxed condition to characteristically hydrophobic textile fibers.

The bundle of fibers prepared and treated according to the foregoing was observed to be very bulky and voluminous for the number of fibers involved. It wa observed with the naked eye that the fibers had a pronounced crimped appearance. When viewed under a microscope it was observed that the individual filaments had taken on a general helical crimp along the fiber axis and the bundle of fibers resembled the schematic portrayal thereof in the sole figure of the attached drawing. The fibers were excellently resilient and exhibited excellent crimp retention after being extended. The percent crimp of the fibers was about 14 percent .and the crimps per lineal inch of the fibers was measured to be about 10. Additionally, the physical properties of the thus crimped fibers were unimpaired when compared to control fibers that were prepared by wet spinning, was-hing, stretching and irreversibly drying under the same conditions (i.e., without the caprolactam treatment, mild drying and dyeing or treating in a hot aqueous medium prior to irreversible drying).

Moreover, when fibers are prepared according to the method of the present invention excepting to eliminate the caprolactam from the aqueous solution, the resulting fibers are essentially uncrimped, appearing rather straight and unbulked much the same as the above mentioned control fibers.

What is claimed is:

1. A method for preparing acrylonitrile polymer fibers having a naturally formed crimp from wet spun fibers of a polymerized ethylenically unsaturated monomeric material containing at least about weight percent polymerized acrylonitrile comprising (a) orienting and then impregnating said fiber while it is in a gel state and in a relaxed condition with an aqueous solution containing between about 5 and about 100 weight percent of caprolactam, based on solution weight;

(b) mildly drying said impregnated gel fiber in a relaxed condition at a temperature between about 20 and about 80 C.;

(c) contacting said mildly dried gel fiber while said fiber is in a relaxed condition, with a hot aqueous medium maintained at a temperature of at least about 60 C.; and,

(d) subsequently, irreversibly drying said gel fiber in a relaxed condition at a temperature between about 100 and 150 C. to a synthetic textile fiber.

2. The method of claim 1, wherein said fiber is wet spun from an aqueous polyacrylonitrile-dissolving zinc chloride solution.

3. The method of claim 1, wherein said acrylonitrile polymer is polyacrylonitrile.

4. The method of claim 1, wherein said aqueous caprolactam solution contains between about 15 and 30 weight percent caprolactam.

5. The method of claim 1, wherein said aqueous medium of part (c) is water maintained at about to C.

6. The method of claim 1, wherein said gel fiber is irreversibly dried at a temperature between about and C.

7. A method for preparing acrylonitrile polymer fibers having a naturally formed crimp which comprises (a) extruding a polymer of a polymerized ethylenically unsaturated monomeric material containing at least about 80 weight percent polymerized acrylonitrile dissolved in an aqueous zinc chloride solution into an aqueous zinc chloride coagulating bath to form a gel filament of said polymer;

(b) washing said gel filament essentially free of residual zinc chloride and orienting said gel filament;

(c) immersing said washed and oriented gel filament while it is in a relaxed condition in an aqueous solution containing between about 5 and about 100 weight percent caprolactam, based on solution weight;

(d) mildly drying said gel filament in a relaxed condition at a temperature between about 20 and about 80 C.

(e) immersing said mildly dried gel filament while it is in a relaxed condition in an aqueous bath of about 90 to 100 C.; and,

(f) subsequently, irreversibly drying said gel fiber in a relaxed condition at a temperature between about 130 and 140 C. to a synthetic textile fiber.

References Cited UNITED STATES PATENTS 2,917,805 12/1959 Rokosy 264--l68 2,988,420 6/1961 Ryan et al 264168 3,122,443 2/1964 Blankenship 264182 ALEXANDER H. BRODMERKEL, Primary Examiner.

D. J. ARNOLD, Assistant Examiner. 

1. A METHOD FOR PREPARING ACRYLONITRILE POLYMER FIBERS HAVING A NATURALLY FORMED CRIMP FROM WET SPUN FIBERS OF A POLYMERIZED ETHYLENICALLY UNSATURATED MONOMERIC MATERIAL CONTAINING AT LEAST ABOUT 80 WEIGHT PERCENT POLYMERIZED ACRYLONITRILE COMPRISING (A) ORIENTING AND THEN IMPREGNATING SAID FIBER WHILE IT IS IN A GEL STATE AND IN A RELAXED CONDITION WITH AN AQUEOUS SOLUTION CONTAINING BETWEEN ABOUT 5 AND ABOUT 100 WEIGHT PERCENT OF CAPROLACTAM, BASED ON SOLUTION WEIGHT; (B) MILDLY DRYING SAID IMPREGNATED GEL FIBER IN A RELAXED CONDITION AT A TEMPERATURE BETWEEN ABOUT 20* AND ABOUT 80*C.; (C) CONTACTING SAID MILDLY DRIED GEL FIBER WHILE SAID FIBER IS IN A RELAXED CONDITION, WITH A HOT AQUEOUS MEDIUM MAINTAINED AT A TEMPERATURE OF AT LEAST ABOUT 60*C.; AND, (D) SUBSEQUENTLY, IRREVERSIBLY DRYING SAID GEL FIBER IN A RELAXED CONDITION AT A TEMPERATURE BETWEEN ABOUT 100* AND 150*C. TO A SYNTHETIC TEXTILE FIBER. 